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Comment by sidkshatriya | Hacker News Reader

From what I've understood from previous discussions (don't know much about plasma physics though): It is a multistep challenge. Step 1: Figure out how to get a self-sustaining fusion reaction. Step 2: figure out how to extract the energy in a useful, safe, non-destructive (to the reactor) way.

Doing Step 1 alone is very difficult so the've postponed Step 2 to the future. I may be wrong though.

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I would imagine since, combined, we're spending tens of billions of dollars on Fusion research - someone must have some ideas for step 2, right?!

We have some ideas, of course. The rough idea is: surround the reactor with a lithium blanket. This gets bombarded with neutrons, breeding fuel and heating the lithium, which transfers its heat to coolant to spin turbines. The devil is in all the engineering details, like: how do we make alloys to deal with neutron bombardment/hydrogen embrittlement, what's the optimal geometry to capture flux while being serviceable, etc.

Much of that work can and is researched in parallel, but there will be inevitable integration hell that has a burning fusion reactor core as a prerequisite.

What is done with the “spent” lithium blanket? Is it radioactive waste?

It depends on how it’s engineered. The lithium itself wouldn’t be “radioactive waste” but the vessel for the lithium would likely be.

There are currently major unsolved problems with step 2.

https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/...

10s of billions... Over many decades. We spend very little on fusion research overall.

ITER itself costs $21B (over a decade).

Globally we are definitely spending $10B+ per year.

Step 3: Profit

Nothing wrong with Step 3: Profit (not that you said anything negative about it).

The promise of profit often helps enables all the previous steps.

Long term research can lead to eventual profit, sometimes many decades later. Sometimes it does not.

Long term research is speculative investment -- high risk for high reward.

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